Project summary/abstract Previous studies, conducted both in the US and other countries, have found that women who deliver their first child by cesarean section are less likely to bear subsequent children and bear fewer subsequent children than women who deliver their first child vaginally. However, nearly all of these studies were retrospective analyses of existing data sets, or surveys of women years after their first delivery. Consequently, it is not clear if women who deliver their first child via cesarean section are different from women who deliver vaginally prior to the first delivery in ways that both predispose them to require delivery by cesarean section and to be less likely to want to or be able to conceive and bear one or more subsequent children, or if there is something about the cesarean section itself that affects women's desire or ability to conceive or bear subsequent children. Given the recent increase in the rate of cesarean section in the US and in countries throughout the world, it is essential that well-designed, carefully conducted, prospective, longitudinal studies with adequate statistical power be conducted to improve scientific knowledge of the extent to which cesarean section increases a woman's risk of subsequent infertility, and if so, why. This prospective, longitudinal study of child-bearing patterns in relation to mode of first delivery is an investigation of both factors that increase a woman's risk of delivering her first child by cesarean section, and the effects of primary cesarean delivery on important outcomes, including subsequent child-bearing. The specific aims of this study are: 1.) To measure pre-first delivery child-bearing desires and intentions among a diverse sample of 2790 pregnant women through interviews designed to assess pre-delivery factors that could explain post-cesarean deficits in subsequent child-bearing, 2.) To measure labor and delivery related factors in the hospital medical records of these 2790 women that could explain post-cesarean deficits in subsequent child-bearing, and 3.) To determine the effects of primary cesarean delivery on subsequent childbearing, via a 3-year prospective, longitudinal study of these 2790 women, with assessments at 1, 6, 12, 18, 24, 30 and 36 months post first delivery, comparing those who deliver by cesarean section to those who deliver vaginally, taking into account factors measured in the pre- delivery interview and the hospital medical records. Project Narrative The rate of cesarean delivery in the US has increased dramatically in the past decade and more than a million women deliver by cesarean section annually. This study will investigate the extent to which cesarean delivery increases a woman's risk of subsequent infertility and will substantially improve the current level of scientific knowledge about this issue.